Method for setting well conduit with passages through conduit wall



1962 M. A. MALLINGER 3,057,405 METHOD FOR SETTING WELL CONDUIT WITHPASSAGES THROUGH CONDUIT WALL Filed Sept. 3, 1959 INVENTOR;

MORTON A. MALLINGER Mfiim ATTORNEY United States Patent Ofltice3,057,405 Eatented Get. 9, 1962 3,057,465 METHOD FOR SETTING WELLCONDUIT WITH PASSAGES THROUGH CONDUTT WALL Morton A. Maiiinger, Tuisa,Okla, assignor to Pan American Petroicum Corporation, Tuisa, Okla, acorporation of Delaware am Filed Sept. 3, 195?, Ser. No. ca ses 3Claims. (Cl. 16625) This invention relates to completing Wells. Moreparticularly, it relates to placing a conduit in a well and formingopenings through the wall of said conduit through which fluids can flowinto the conduit.

In the drilling of wells for the production of oil or gas, aconventional procedure is to drill through the prospective producingformation and then run a string of metallic easing into the well andthrough the formation. The casing is then cemented in the conventionalmanner to seal off the prospective producing formation from underlyingor overlying formations containing water or gas. Thereafter, the metalcasing is perforated by means of bullets or shaped explosive charges.These pierce the pipe and cement sheath and penetrate into thesurrounding earth formations to provide channels through which oil andgas can enter the casing.

Such methods have been very successful. They are, however, quiteexpensive. In addition, the holes through the casing are generallysmall. They provide little flow capacity for liquids flowing from theformation into the well. The restriction is particularly serious whenfluids are forced out through the holes at high rates in order tofracture the surrounding formation.

Efforts to overcome such difliculties have included the use of weakenedsections of the casing which can be ruptured by the fracturing fluid.Such a system is described in US. Patent 2,642,142 issued on July 16,1953, to J. B. Clark. Other efforts have included the use of sections ofcasing which can be removed by solvents such as acids. Alloys sold undertrademarks such as Securaloy are available for this purpose. Still otherattempts to overcome the difficulties of gun perforating have includedplacing explosive charges in projections extending through and outsidethe casing wall. The explosives, when detonated, form large passagesthrough the casing and projections. An example of this type ofdevelopment is found in US. Patent 2,201,290 issued on May 21, 1940, toH. M. Greene.

All these schemes have their difficulties. For example, if a weakenedsection of the casing is strongly supported by cement, it may be asdiflicult to burst as an unweakened section of easing not supported bycement. There is sometimes danger therefore of bursting the casing atthe wrong level.

The use of solvents may also be successful. Once a small hole forms inthe soluble section, however, the remaining solvent may leak awaythrough the hole to the formations surrounding the section. In thiscase, the first small hole is all that is formed. If the pressureoutside the casing is greater than that inside, fluids from the outsideenter the first small hole diluting the solvent and driving it away fromthe section to be dissolved. Again, only a single small hole may result.In addition, solvents such as acids have at least some solvent action onthe steel casing as well as on the special section to be dissolved. Theuse of expensive operating procedures to dissolve the casing section arealso required, as in the case of the gun perforator.

The use of small charges of explosives placed in the casing wall to blowholes in the casing should be successful in some cases. As noted in theGreene patent referred to above, however, explosives are thermallysensitive. Placing such explosives in deep wells may result d inpremature detonation of the explosive by the high temperatures of suchwells before the casing can be cemented in place. Many explosives arenot operable under high pressures in wells. There may be some difficultyfrom this standpoint. The principal difficulty however is that the outerside of the chamber which holds the explosive is supported by theformation or the cement outside the casing. The inner wall is notsupported. Therefore, as often as not, detonation of the explosiveremoves the inner Wall Without bursting the strongly supported outerwall.

With the above problems in mind, an object of this invention is toprovide a means for completing a well in which a large passage is formedthrough the wall of a conduit lowered into the well. Another object isto provide a mean for forming a passage through the casing lowered intothe well which means does not require the use of expensive specialapparatus or manipulations. Still another object is to provide apparatusspecially adapted for simple inexpensive well completion operations inwhich a passage through a well conduit wall is required. Other objectswill be apparent to those skilled in the art from the followingdescription and claims.

My method of completing wells can best be illustrated in connection witha casing cementing operation. In this case, a section of casing isprovided which has projections sticking out of it. A passage is providedthrough the casing wall and through the projections. The outer end ofthe passage is plugged by a material which can be melted in any ofseveral ways. The casing is run into the well, with the special sectioninserted at the proper point to be set opposite a producing Zone of thewell. After the casing is lowered into the well, it is cemented inplace. The plug is then melted out of the end of the passage to form anopening extending from the formation to the interior of the casing.

My invention will be better understood by reference to the drawing inwhich:

FIGURE 1 is a cross-sectional view of a well showing an embodiment of myinvention in which a section of casing has projections containingpassages plugged at their outer ends with a material which can be meltedto open the passages.

FIGURE 2 is a detailed View in cross-section of one form of a projectionwith a plug in its outer end.

FIGURE 3 is another detailed view in cross-section showing a form ofprojection in which the plug in the outer end is reinforced to preventpremature collapse.

FIGURE 4 is a cross-sectional View of another form of projection inwhich a reservoir is provided for the molten plug so this material willnot enter the well.

FIGURE 5 is a view of a section of casing in which the projections aresupported by webs extending along the casing.

In FIGURE 1, a well 10 penetrates an oil producing sand 11. A string ofcasing 12 has been lowered into the well. This casing includes a sectionhaving projections 13 extending outwardly. The section bearing theprojections is set opposite the producing formation. An electric heater14 is shown lowered into the casing on electric cable 15.

The character of the projections can be seen in more detail in FIGURE 2.Here, the projection 13 is a tube extending through casing 12. The tubeis attached to the casing by means such as weld 16. The tube is closedat its outer end by a plug 17. The plug is formed from a low-meltingalloy.

In using the apparatus shown in FIGURES 1 and 2, the casing is loweredinto the well until the special section is opposite the producingformation. The casing is then cemented in place by running a string oftubing into the well with a packer on the bottom, setting the packerbetween the casing and tubing near the bottom of the casing string, andpumping Portland cement slurry down the tubing and up around the outsideof the casing. After the cement is set, the tubing is withdrawn and theheater is lowered through the section opposite the prOduCing formationto melt the alloy plugs at the ends of the tubes and permit flow offormation fluids into the casing from which it can be removed to thesurface of the earth by pumps or other well-known means.

The alloy should have a low melting point. If the casing is heated to atemperature very much above about 700 F., the cement behind the casingmay be seriously damaged. The critical temperature of water is about 700F. Temperatures above this value may seriously interfere with hydrationof the cement as well as adversely affecting the bond between the cementand the casing. For these reasons, the plugs in the passages through thecasing and projections should have a melting point which is not aboveabout 700 F. Preferably, the melting point should be no more than about100 F. above the normal static temperature of the formation oppositewhich the special section of casing is to be set. This is to decreasethe amount of heat which must be generated to melt the plugs.

The trouble of running a tubing string for the cementing job can beavoided by pumping cement down the casing itself. In this case, however,the passages through the casing and projections should be eithercompletely filled with the low-melting alloy or at least the passagesshould be plugged at both the outer and inner ends.

While the above-described method represents one embodiment of myinvention, it is not the preferred or most advantageous form. The use ofthe heater is certain and convenient, unlike some of the techniques withexplosives and solvents. Nevertheless, it does involve the extra step oflowering the heater into the well. This step can be avoided in two ways.In shallow wells, water or other liquid can be circulated in the wellbefore the casing is run. Experience has shown that the bottom holetemperature can be lowered about 40 F. by circulating a liquid such asdrilling fluid in the well. About eight hours are then required for thetemperature to rise to the normal static bottom hole value. This makespossible a process with certain advantages. In this process, a coolliquid is first circulated in a well to decrease the bottom holetemperature by about 40 F. The liquid temperature must be at least about50 F. below the normal static bottom hole temperature for this purpose.The circulation is made through a string of tubing or drill pipe in thewell. After several hours of circulating, preferably at least abouteight hours, the tubing or drill pipe is withdrawn and the casing stringis immediately run into the well. The special section of the casing,which includes the plugged passages, is set opposite the producingformation as before. Again, Portland cement is placed outside thecasing. In this case, however, the plugging material in the ends of thepassages has been selected with unusual care.

The melting point of the material lies somewhere between about 20 F.below the normal static bottom hole temperature and about 20 F. abovethe normal static bottom hole temperature.

The bottom of the well slowly warms to normal static bottom holetemperature. In addition, the cement generates considerable heat whilesetting. The combination of the two heat sources raises the casingtemperature to a value of at least about 20 F. above normal staticbottom hole temperature, about eight hours after the cement isintroduced. This is suificient to melt the plugs in the passages throughthe casing. It will'be noted that in this process, openings of anydesired size are formed through the casing wall with no manipulativesteps, with one exception, beyond those normally used in a cementingoperation. This exception is the initial simple circulating step.

The melting point of the plugging material should be no lower than 20 F.below the normal static formation temperature event though the welltemperature is lowered to 40 F. below the normal static value bycirculation. This is to allow a factor of safety. The well beginswarming up during the withdrawal of the circulation conduit and therunning of the easing into the well. If any delay is encountered afterthe casing is in place in the well but before the cementing operationbegins, the well can be kept cool by slowly circulating a cool liquidthrough the casing. As soon as circulation of the cement slurry isinitiated, this slurry cools the well and prevents premature melting ofthe plugs in the passages.

Even the circulating step can be avoided in the preferred embodiment ofmy invention. In this case, the material used to plug the passagesthrough the casing wall is even more carefully selected. It has amelting point slightly above the normal static temperature of theproducing formation opposite which the special section of casing is tobe set. The melting point of the plug should be between the normalstatic temperature of the producing formation and a temperature about 20F. above this normal static temperature. Since the melting point isabove the normal static temperature, no cooling of the well is requiredbefore the casing is lowered into place. The plugging material is meltedsolely by the heat generated by the cement in setting. Again to allow asafety factor, the melting point should usually be at least about 5 F.above the normal static formation temperature.

In this preferred embodiment, the projections on the outside of thecasing become very important. FIGURE 1 of the drawing shows theprojections on one side of the casing lying against the well wall. Thisis the usual case. A well is almost never absolutely vertical.Therefore, the casing almost always lies against the well wall on oneside. In the absence of the projections, the casing itself would beagainst one wall. On this side, little, if any, cement could existbetween the casing and the well wall. Therefore, little heat could begenerated and the plugs and the passages on that side might not melt.With projections extending outwardly at least about an inch from thecasing wall, however, adequate cement is provided to raise the casingtemperature at least about 20 F. or more above the normal staticformation temperature.

Centralizers could, of course, be used to hold the casing away from thewell wall as in ordinary cementing practices. In the case of myinvention, however, it is preferred that centralizers other than theprojections should not be used. In this connection the other importantpurpose of the projection is to be noted. In holding the casing awayfrom the well wall, the projection itself is pressed against the wellwall. Therefore, when the plug is melted from the passage, a clearopening is provided on at least one side of the casing from the interiorof the casing through the cement to the formation. If centralizers otherthan the projections are used, there is some chance that at least a thinfilm of relatively impermeable cement may be outside all the passages. Ahydraulic fracturing operation, which preferably follows my method, willgenerally burst through any cement films, but fracturing is much simplerif the permeable formation itself is exposed to the end of the passage.

If the projections are to be used as centralizers, it will be apparentthat they will drag along the well wall. To decrease the danger ofknocking off some of the projections, they should be reinforced as shownin FIGURE 5. In this figure the projections 13 on casing 12 aresupported by webs 20 extending along the casing.

Many diiferent types of materials may be used to plug the passagesthrough the casing wall. Some inorganic solids have melting points inthe desired range. These include the hydrated nitrates such as those ofchromium, iron, mercury, and nickel. Most of the low-melting inorganicsalts are too water soluble for general use however.

Crude organic materials, such as paraffin, gilsonite, beeswax and thelike, may be used if one can be found which has the required strengthand the close melting range at the desired temperature for a particularWell. If organic materials are used however, it is preferred thatrelatively pure compounds be employed. Table 1 presents a list of purecompounds having, sharp melting points. Most of these materials arereadily available. Their melting points are distributed throughout therange from about 100 F. to about 300 F. which is of most interest incasing oil wells.

Table 1 Material: M.P., F. Phenol 1 108 Paratoluidine 113 Cetylmercaptan 122 Paradichlorobenzene 127 'Orthophenylphenol 136 Palmiticacid 14-4 Stearic acid 156 Biphenyl 158 Glyceryl tristearate 160 Methylbeta-naphthyl ether 162 Naphthalene 176 Ethylene iodide 180Paradibromobenzene 192 Tribenzyl amine 196 Alpha-naphthol 201Phenoxyacetic acid 205 Phenanthrene 212 Catechol 219 Beta-naphthyl amine234 Acetanilide 237 Benzoic acid 250 Maleic acid 266 Urea 270Paratoluene sulfonamide 279 Parachlorobenzene sulfonamide 291 Adipicacid 306 Citric acid 307 Salicylic acid 315 Still other organicmaterials will occur to those skilled in the art. Many references, suchas The Systematic Identification of Organic Compounds by Shriner, Fusonand Curtin, 4th edition, published by John Wiley and Sons, Inc., listlarge numbers of materials by their melting points, permitting selectionof appropriate materials to fit almost any particular situation.

Most of the materials listed in Table 1 are crystalline solids withconsiderable strength. It is possible, however, that they may notwithstand the pressure difierences across a casing wall. This isparticularly true when the casing is run with a float shoe which resultsin a high hydrostatic pressure outside the casing and little, if any,pressure inside. In such cases it may be advisable to taper the passagesshown in FIGURE 2 so that the internal diameter of the tube 13 issmaller at the inside end opening into the casing than at the outer endextending outside the casing. Thus, if the plug tends to move inwardlyfrom the outer end of the passage, its motion is stopped by the taperedshape of the opening.

Still another reinforcing scheme is illustrated in FIG- URE 3. Here, thetube 13 has at its outer end a strong metallic plate 21 withperforations 22 plugged with the low-melting material. The reinforcingmember 21 may also take the form of a multiplicity of webs or platesextending across the outer end of the passage. Still other reinforcingmeans Will occur to those skilled in the art. (It will be apparent thatwhen reference is made to the ends of passages being closed by amaterial having a melting point within a certain range, this is intendedto include plugs containing reinforcing elements of materials meltingabove the specified range.

By far the most preferred type of material to be used as plugs for mypurposes is an allow such as Woods metal. Recently, eutectic mixturescontaining indium have become commercially available. These, with thewell-known eutectic mixtures of lead, bismuth, tin, and cadmium, form aseries of alloys with melting points distributed throughout the desiredtemperature range. Table 2 summarizes some of these eutectics.

Table 2 Eutectic M.P., Bis- Lead Tin Oad- Thal- Indium I mut mium liumThe above information is taken from handbooks and encyclopedias and doesnot represent original data by the inventor. Other eutectic compositionsexist and will become commercially available in the future. All theabove compositions have sharp melting points since they are eutecticcompositions. Other alloys which are not eutectics can be used ifdesired as long as the range of temperatures between the all-solid andcompletely-liquid states is not too great. This range must besufficiently narrow to permit adequate flow of the alloys to open thepassages to flow of treating solutions from within the casing, or offormation fluids from outside the casing.

Many of the low-melting alloys are soft and weak. Therefore, it is oftenadvisable to provide supporting perforated plates as shown in FIGURE 3.Supporting webs may also be used as described in connection with theorganic plugging materials.

In FIGURE 4 of the drawing, two additional features of my invention areillustrated. Tube 13, in this case, has a raised portion 23 on the lowerside of the inner end. The purpose is to prevent entry of the moltenplugging material into the casing. in most cases the plugging materialwill have a melting point slightly higher than normal static bottom holetemperature. When this material melts. due to the heat developed bysetting of the cement, it ordinarily runs down the inner wall of thecasing to the bottom of the well. The small amount of material usuallywill not interfere with subsequent well operations. This is particularlytrue if the plugging material is relatively soft. If a fairly strong,hard alloy is used, however, and if the melting point is near the toptemperature developed by the cement, the plugging material may not havea chance to run very far down the casing before it becomes solid. Ifthis happens, the alloy from each projection will form a bump on theinside surface of the casing. These bumps may interfere to some degreewith future manipulations of well tools in the casing. If a tube, asshown in FIGURE 4, is used, however, raised portion 23 holds the moltenmaterial in the tube itself and does not permit it to flow into thecasing.

As also shown in FIGURE 4, the plugging material may be threaded. Thisis to permit easy insertion of the particular plugging material selectedfor use in a specific well. By useof such inserts, the casing sectionitself can be made up as a standard item. Discs of plugging material ofvarious melting points can then be carried along to wells where theproper ones applicable to the particular well can be selected andscrewed into the projections from the casing. Still other designs ofreplaceable plugs will occur to those skilled in the art.

To this point, my invention has been described in connection with casingcementing operations in which Portland cement is used as the cementingmaterial. My invention is capable of several variations. For example, ifthe cementing material is a cold-setting plastic, no heat will begenerated. The embodiments of my invention involving precirculation ofthe well to cool it or the use of a heater lowered into the well arestill applicable.

Means other than electric heaters can also be used to melt out theplugs. For example, a mixture of magnesium and hydrochloric acid may beintroduced into the well opposite the zone where heat is required.Methane and air may also be conducted to the botom of the Well wherethey are ignited to produce the desired heat. Still other means will beapparent to those skilled in the art.

My invention even has some applications outside the field of casingcementing operation in wells. For example, it may be desired to place aslotted liner or screen in a well producing sand to exclude the sandfrom the pump. In such cases, the holes or slots in the liner or screenmay be filled with a plugging material to facilitate washing the screeninto a gravel pack, to permit circulating sand and mud from the bottomof the well, or for other purposes. Examples of such filled liners areshown in U.S. Patent 2,401,035 issued to S. M. Akeyson et al., on May28, 1946.

In accordance with my invention, the slots of such liners or screens arefilled with a material having a melting point slightly below thetemperature of the formation opposite which the screen is to be set. Astring of tubing is run into the well, a cool liquid is circulated inthe well to lower the temperature to a point below the melting point ofthe plugging material. A batch of gravel is next placed in the bottom ofthe well. The tubing is then withdrawn, the plugged liner is placed onthe bottom of the tubing and the tubing string is run into the wellagain. Water is circulated through the tubing and the open bottom end ofthe plugged screen to wash the screen into the gravel. After thisoperation, the well is held shut in for about eight hours to permit thewell temperatures to rise to their normal static levels. The pluggingmaterials in the slots of the screen are thus melted, opening the screento the flow of formation fluids.

An example of the application of my invention to cementing casing in awell is as follows: The well is 5,000 feet deep and at the bottom is 9inches in diameter. Casing /2 inches in external diameter is to be runto the bottom. An oil producing formation is known to be present from4,950 to 4,980 feet.

A 30-foot section of easing such as that shown in FIG- URE l is made up.The plugs in the ends of the projections are of the replaceable typeshown in FIGURE 4. These projections extend outwardly 1 inch from theoutside surface of the casing. They are set 1 foot apart along thecasing in four rows arranged equally around the easing. The passagesthrough the casing and projections are 1 inch in diameter.

At the well, a recording thermometer is run to 4,980 feet. The formationtemperature is found to be 150 F. Alloy number 8 in Table 2 is selectedas the plugging material anddiscs of this material are screwed into thesection 20 feet from the bottom of the string. The casing is thencemented in place with a slurry of Portland cement. The well is heldshut in for eight hours to permit the cement to set and to melt out theplugs in the passages.

outer ends of the passages through the casing wall and After waiting atleast 72 hours for the cement to develop a greater strength, a hydraulicfracturing operation is carried out through the open passages and thewell is placed on production.

It will be apparent from the above description that my invention iscapable of many variations. I do not, therefore, wish to be limited tothe above specific examples but only by the following claims.

I claim:

1. A method for completing a Well penetrating a producing formationcomprising circulating for several hours past said formation in saidwell a liquid at least about 50 F. cooler than the normal statictemperature of said producing formation, immediately running casing intosaid well, said casing including a section, set opposite said producingformation, which has a projection extending outwardly from said casingand a passage extending through said projection and the wall of saidcasing, the outer end of said passage being plugged by a material havinga melting point in the range between a temperature about 20 F. below thenormal static temperature of said producing formation and a temperatureabout 20 F. above the normal static temperature of said producingformation, placing Portland cement outside said casing at the level ofsaid formation and holding said well shut in for at least about eighthours to permit the heat from the formation and from the setting of thecement to melt the plug in said passage.

2. A method for completing a well penetrating a producing formationcomprising circulating for several hours past said formation in saidwell a liquid at least about 50 F. cooler than the normal statictemperature of said producing formation, immediately running casing intosaid well, said casing including a section, set opposite said producingformation, which has a projection extending outwardly from said casingand a passage extending through said projection and the wall of saidcasing, the outer end of said passage being plugged by a material havinga melting point in the range between the normal static temperature ofsaid producing formation and a temperature about 20 F. below said normalstatic temperature of said producing formation, placing a cementingmaterial outside said casing and holding said well shut in for at leastabout eight hours to permit the heat from the formation to raise thecasing temperature to the normal static formation temperature and thusmelt the plug in said passage.

3. A method of completing a well opposite a producing formationcomprising circulating for several hours past said formation in saidwell a liquid at least about 50 F. cooler than the normal static bottomhole temperature of said well, immediately lowering a conduit into saidwell, said conduit including a section having a passage extendingthrough the wall of said conduit, said passage being plugged by amaterial having a melting point in the range between the normal statictemperature of said formation and a temperature about 20 F. below thenormal static temperature of said formation, and holding said well shutin for at least about eight hours to permit the heat from the formationto raise the conduit temperature to the normal static formationtemperature and thus melt the plug in said passage.

References Cited in the file of this patent UNITED STATES PATENTS2,267,683 Johnston Dec. 23, 1941 2,772,737 Bond et a1. Dec. 4, 19562,775,304 Zandmer Dec. 25, 1956

